Nosema apis

Definition

A microsporidian species (phylum Microsporidia) that parasitizes the midgut epithelium of the western honey bee (Apis mellifera), causing nosemosis—historically the most common and widespread adult honey bee disease worldwide. The pathogen forms environmentally resistant spores that persist in combs, withstand freezing and desiccation, and are transmitted via fecal-oral contamination. Infection reduces worker longevity, impairs foraging efficiency, and can trigger colony depopulation or collapse, particularly during spring buildup when transmission accelerates in crowded hives.

Etymology

New Latin, from Greek nosēma 'disease' + Latin apis 'bee', coined by German apiculturist Enoch Zander in 1909.

Example

Beekeepers in temperate regions routinely sample for Nosema apis spores by hemocytometer counts of worker midgut homogenates, with thresholds above one million spores per bee indicating treatment need; however, many operations now encounter Nosema ceranae as the dominant pathogen, which produces higher spore loads and more severe colony-level impacts.

Related Terms

• Nosema ceranae
• nosemosis
• Microsporidia
• honey bee pathology
• apiary
• gut parasite

Usage Notes

Historically conflated with 'nosema disease' generally; since the 2000s, Nosema ceranae has largely displaced N. apis as the primary nosema pathogen in many regions, though both may co-occur. Spore morphology alone cannot distinguish the two species—molecular diagnosis (PCR) is required. The OIE (now WOAH) lists nosemosis as a notifiable disease of honey bees.